If confirmed, it might also be within range of future observatories.

A reanalysis of old data obtained by an Earth-based observatory has found what seems to be the signal of a large planet, somewhere between the mass of Earth and Neptune, orbiting a dwarf star about 42 light years from Earth. It's part of a crowded system of six planets, but appears to be the only one of them that's in the host star's habitable zone. And, according to the people who have identified it, the planet should be close enough to Earth to be imaged directly by some of the observatories currently in the planning stages.

The star in question is HD 40307, which is only about three-quarters the mass of the Sun, and quite a bit dimmer. The star has been targeted for observations using the HARPS, the same instrument that recently spotted the signal of an exoplanet in the Alpha Centauri system. The instrument looks for periodic changes in the light emitted by the star. These arise from Doppler shifts caused by its orbiting planets, which periodically pull the star in different directions.

The HARPS team had already analyzed data from HD 40307, and determined that there were three planets apparent in the data obtained by the instrument. But now, an international team of researchers has gone back and reanalyzed the data using a number of different methods. Their work suggests there are at least six planets in the system.

The HARPS method of finding planets is extremely sensitive to noise, since things such as the star's rotation can also cause periodic changes in the light we receive from it. For short-term changes, the initial HARPS analysis simply combined a series of measurements taken at short intervals, figuring that any noise should average out.

The new analysis relies on a revised data set, obtained after a potential source of error in the HARPS measurements was identified and accounted for. It also skips merging the data, and uses a somewhat different statistical method to analyze matters.

After identifying and eliminating a couple of sources of periodic noise—including the star's rotation and its activity cycle—the authors set down to identifying signals from any orbiting planet. The technique they use is pretty standard in papers like this: identify the signal of one orbiting planet, remove it, and look for whether any additional signals are left. Signals are identified by modeling the effect you'd see by having planets of various masses orbit at all possible distances out to a limit.

As you might expect, the initial three planets spotted by HARPS created clear signals in the data. As they were removed, however, additional signals kept becoming apparent, with orbital periods at 34, 51, and 320 days. Using unmerged data, this six planet version of the system was far more probable than the three planet one that had been originally proposed.

But the researchers weren't done yet. Variations in light emitted by the star are more pronounced at shorter wavelengths than at longer ones (towards the red end of the spectrum and beyond). So to avoid some of the noise, they went back and reanalyzed the unmerged, noise-corrected HARPS data, focusing on the red end of the spectrum this time. The same 34 and 51 day signals were still there, but now the 320 day signal was weaker, replaced by one at 200 days. It turns out that, due to the periodicities involved, these two signals can partially overlap, and the authors suggest that a combination of noise and the signals' similarity led to the initial, mistaken identification.

That shift in distance makes a dramatic difference, as a 200 day orbit places the planet squarely in the zone expected to have liquid water. Because of the relative dimness of the host star, the habitable zone is quite a bit closer in than it is near the Sun, covering between 0.43 and 0.85 Astronomical Units (the typical distance between the Earth and Sun).

The planet itself is about seven times the mass of Earth, placing it in an awkward position between being a super-Earth (a massive, rocky body) and a mini-Neptune, which is a watery/gaseous body. Without knowing more about the planet, it's tough to discriminate between these choices. They suggest that planetary modelers might want to consider the conditions that would prevail there for both of these options.

They also note that several telescopes that are in the planning stages would be able to resolve the planet (assuming they go forward), and will be able to potentially tell us something about their composition. In the mean time, follow up observations should give us a better sense of whether the signal identified in this reanalysis is actually caused by a planet. It took a lot of statistical effort to reveal it, and the authors' own calculations suggest that this tightly packed system of six planets would only be stable under a limited number of scenarios (nearly circular orbits, limited mass ranges of the planets, etc.) So, although the analysis the authors did here is perfectly reasonable, it would be nice to see it hold up when further data comes in.

With all the data collected over the years for various projects, I have to wonder how many people have looked straight through some amazing discovery and declared their project a failure simply because they were looking at the information from the wrong mental perspective? Makes me think of a section in "How I Killed Pluto and Why It Had It Coming" where the author went through all the photographic plates taken by an earlier astronomer. Each of them were looking for one specific thing in those plates, and who knows what they glossed over in their tightly focused gaze.

OK I have a question - Why don't we ever send a space probe into a gas giants atmosphere AND take pictures while it descends? All my life I've been obsessed with space, and have always wondered what it looks like inside a gas giant.

I remember seeing pictures of the inside of Jupiter when I was in elementary school, that were apparently from the Juno spacecraft as it plunged into the atmosphere. I've never been able to find those pictures again, and my research into the Juno probe didn't mention getting pictures while it was descending, so I'm assuming they were computer generated images.

Still, the idea is cool. Are there technical limitations as to why it hasn't been done? We've had multiple opportunities to do it, you'd think someone at NASA would say "Hey, we're gonna crash the probe into the planet anyways, why not slow its descent so it can survive entry and take some pictures on the way down?"

OK I have a question - Why don't we ever send a space probe into a gas giants atmosphere AND take pictures while it descends? All my life I've been obsessed with space, and have always wondered what it looks like inside a gas giant."

The Galileo mission dropped a probe into the Jovian atmosphere. The re-entry heat destroyed a large fraction of its heat shield. Nonetheless there were instruments onboard that operated for ~1 hr. No photographic cameras that I'm aware of.

OK I have a question - Why don't we ever send a space probe into a gas giants atmosphere AND take pictures while it descends? All my life I've been obsessed with space, and have always wondered what it looks like inside a gas giant."

The Galileo mission dropped a probe into the Jovian atmosphere. The re-entry heat destroyed a large fraction of its heat shield. Nonetheless there were instruments onboard that operated for ~1 hr. No photographic cameras that I'm aware of.

Right! Do I have Galileo and Juno confused? Or was Juno the probe attached to Galileo? Can't quite remember.

That would have been a prime opportunity to see inside a gas giant. Imagine the colors and pillars of gas etc. It would truly be an amazing sight IMO.

Is this meaning all six planets have no moons? Because I understand the gravitational pull from the moons: #1. They can't be too closer from one another if moons around. #2. These planets can't be "nearly circular orbits" around their host star because of the gravitational pull from the moons. These planets and the host star are getting too old in age. Their conditions may be the same as Mars. There is not much of an atmosphere there and having low and may be none magnetic field to protect these planets from the impact of foreign objects. Like Mars water once there but has been gone long ago? (Too early for the conclusion..?)

Where can I find the actual research paper that this article is based on? Sources...

There is a DOI link in the bottom, but it's not yet available. It usually takes a while, just wait for a bit...

As to why we don't send cameras to gas giants, I'm guessing it's the same problem: $. Cameras are cool and all, but they yield little scientific results. At least that's what some astronomers said to me...

It wasn't so long ago where religious people claimed that there were no other planets in the universe. All these reports of Super-Earths make me quite hopeful of astronomers finding a planet that is almost identical to our Earth.

What you wouldn't survive is a pub fight with one of the superearth colonists (those hyper-g chickens walked out of the centrifuge 3 times stronger than their regular siblings)...

Are those chickens real?

Off topic: I was happy about finding a possible home for the Elcor until I remembered ME3. I understand a lot of people like it but still... I used to think Saren looked like a cute cat with a personality problem. They should have ended 3 with the appreance of G-man.

This planet around an M star is likely not tidal locked, according to other descriptions. I am general skeptical to the idea that tidal lock is a serious impediment for habitability. But it is an often promoted hypothesis.

Hence it is nice to see that not only do we observe non-tidal locked habitables around red dwarfs, but the current ratio of non-locked to possibly locked red dwarf (M star) habitables is ~ 20 %. (One of the Gliese habitables in The Habitable Exoplanet Catalog is a K star.)

The statistics is meager, and the biases of the various methods used is still very much constraining it.

However, it is already pretty safe to note that since M stars are the most common stars and are expected to have many terrestrials (see the current HEC statistics), this means many by all acceptable ("certified") habitables around M stars.

What would surface gravity be like on a planet like this? Uninhabitable?

The physics works out so that it is a relatively low surface gravity, see previous comments.

In general gravity is not much of a problems for cells, as evidenced by life existing several km down oceans and crust. Since the pressure and/or gravity is relatively evenly distributed, they can resist large total pressures/gravities.

Differential forces are more of a problem. Many bacteria have membrane wall cages between dual membranes reminding of floorball balls, and can resist osmotic differentials of ~ 40 atmospheres. Similarly, multicellular life can resist some differential forces, rocket sled experiments gets up to ~ 40 g's and a fetus can survive shocks of 1000s of g's when surrounded by and imbibing uterine fluid.

The problem would be skeletons/shells and movement. But I would expect multicellulars could resist 100s of g's and still be reasonably large. They may have to use a “latch and spring” mechanism for movements, similar to how mantis shrimp claws can accelerate to over 10 000 g's by storing muscle energy for short periods of release. [ http://en.wikipedia.org/wiki/Mantis_shrimp ]

OK I have a question - Why don't we ever send a space probe into a gas giants atmosphere AND take pictures while it descends? All my life I've been obsessed with space, and have always wondered what it looks like inside a gas giant.

I remember seeing pictures of the inside of Jupiter when I was in elementary school, that were apparently from the Juno spacecraft as it plunged into the atmosphere. I've never been able to find those pictures again, and my research into the Juno probe didn't mention getting pictures while it was descending, so I'm assuming they were computer generated images.

Still, the idea is cool. Are there technical limitations as to why it hasn't been done? We've had multiple opportunities to do it, you'd think someone at NASA would say "Hey, we're gonna crash the probe into the planet anyways, why not slow its descent so it can survive entry and take some pictures on the way down?"

As for why it hasn't been done, these missions are expensive and images wouldn't have given as much information. If they give anything at all in the murky atmosphere, as I remember it the usual reply is it was claimed it wouldn't be very meaningful. At the time, the mission overhead is maybe 20 years for construction and cameras technology was bulky. Also, the necessary bandwidth to get anything out before the crafts are destroyed by the pressure and heat wasn't there, it was needed for the basic instruments.

What you wouldn't survive is a pub fight with one of the superearth colonists (those hyper-g chickens walked out of the centrifuge 3 times stronger than their regular siblings).

An example of a freakishly low density (less than water) planet is Saturn, which in fact has a "surface" gravity roughly equal to Earth despite being almost 100x more massive.

This is cool!

I'm curious to know if any chickens suffered long-term health defects that didn't become evident until well after the experiment was over. I also wonder if any chickens with prior health defects were benefited by the high gravity or had their problems amplified by it. Also (as a potential future experiment), what sustained g-force threshold is the limit before it becomes just too much in the long run? So many questions...

I imagine the larger trouble with a high gravity planet isn't so much the effects of the high gravity on people, animals, or cells, but the delta-v required in taking off or landing on that planet. It takes enough energy just to get stuff like the Space Shuttle into orbit - I can't really imagine what it'd be like to try to get off this exoplanet. I figure, though, that if we had the capability to get there, then we'd probably have the engines to get off that planet too (maybe something like a re-labeled form of the ORION project).

Have they identified the mass of the other planets in the system? Is it mostly gas giants? If that is the case and the orbits are tight (close together) then I would guess that this one would be more neptune-like than earth-like. Exciting tho'.

What's going to be funny is if we look close enough and find someone staring back at us.

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If confirmed, it might also be within range of future observatories.

So we're sending an expedition to build an observatory on this newly discovered planet ?

Awesome !!

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It's part of a crowded system of six planets, but appears to be the only one of them that's in the host star's habitable zone.

2 things here:

1 - 6 planets is a crowded system - as compared to what our solar system w/ 9 planets (pluto is a planet - deal) and numerous mini-planets ?

2 - When they determine these "habitable zones" are they refereing to relative regions based on size and type of the Star (sliding scale) or are they doing a direct compare to where the Earth is relative to the Sun ? And with the size of the planet relative to Eartha dn teh size of the star relative to the Sun - won't those factor shift the possibility of a "habitable zone" -- kind of like putting a dolphin in a kiddie pool.